MatrixGraphs.java

package DataStructures.Graphs;

public class MatrixGraphs {

  public static void main(String args[]) {
    AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(10);
    graph.addEdge(1, 2);
    graph.addEdge(1, 5);
    graph.addEdge(2, 5);
    graph.addEdge(1, 2);
    graph.addEdge(2, 3);
    graph.addEdge(3, 4);
    graph.addEdge(4, 1);
    graph.addEdge(2, 3);
    System.out.println(graph);
  }
}

class AdjacencyMatrixGraph {
  private int _numberOfVertices;
  private int _numberOfEdges;
  private int[][] _adjacency;

  static final int EDGE_EXIST = 1;
  static final int EDGE_NONE = 0;

  public AdjacencyMatrixGraph(int givenNumberOfVertices) {
    this.setNumberOfVertices(givenNumberOfVertices);
    this.setNumberOfEdges(0);
    this.setAdjacency(new int[givenNumberOfVertices][givenNumberOfVertices]);
    for (int i = 0; i < givenNumberOfVertices; i++) {
      for (int j = 0; j < givenNumberOfVertices; j++) {
        this.adjacency()[i][j] = AdjacencyMatrixGraph.EDGE_NONE;
      }
    }
  }

  private void setNumberOfVertices(int newNumberOfVertices) {
    this._numberOfVertices = newNumberOfVertices;
  }

  public int numberOfVertices() {
    return this._numberOfVertices;
  }

  private void setNumberOfEdges(int newNumberOfEdges) {
    this._numberOfEdges = newNumberOfEdges;
  }

  public int numberOfEdges() {
    return this._numberOfEdges;
  }

  private void setAdjacency(int[][] newAdjacency) {
    this._adjacency = newAdjacency;
  }

  private int[][] adjacency() {
    return this._adjacency;
  }

  private boolean adjacencyOfEdgeDoesExist(int from, int to) {
    return (this.adjacency()[from][to] != AdjacencyMatrixGraph.EDGE_NONE);
  }

  public boolean vertexDoesExist(int aVertex) {
    if (aVertex >= 0 && aVertex < this.numberOfVertices()) {
      return true;
    } else {
      return false;
    }
  }

  public boolean edgeDoesExist(int from, int to) {
    if (this.vertexDoesExist(from) && this.vertexDoesExist(to)) {
      return (this.adjacencyOfEdgeDoesExist(from, to));
    }

    return false;
  }

  /**
   * This method adds an edge to the graph between two specified vertices
   *
   * @param from the data of the vertex the edge is from
   * @param to the data of the vertex the edge is going to
   * @return returns true if the edge did not exist, return false if it already did
   */
  public boolean addEdge(int from, int to) {
    if (this.vertexDoesExist(from) && this.vertexDoesExist(to)) {
      if (!this.adjacencyOfEdgeDoesExist(from, to)) {
        this.adjacency()[from][to] = AdjacencyMatrixGraph.EDGE_EXIST;
        this.adjacency()[to][from] = AdjacencyMatrixGraph.EDGE_EXIST;
        this.setNumberOfEdges(this.numberOfEdges() + 1);
        return true;
      }
    }

    return false;
  }

  /**
   * this method removes an edge from the graph between two specified vertices
   *
   * @param from the data of the vertex the edge is from
   * @param to the data of the vertex the edge is going to
   * @return returns false if the edge doesn't exist, returns true if the edge exists and is removed
   */
  public boolean removeEdge(int from, int to) {
    if (!this.vertexDoesExist(from) || !this.vertexDoesExist(to)) {
      if (this.adjacencyOfEdgeDoesExist(from, to)) {
        this.adjacency()[from][to] = AdjacencyMatrixGraph.EDGE_NONE;
        this.adjacency()[to][from] = AdjacencyMatrixGraph.EDGE_NONE;
        this.setNumberOfEdges(this.numberOfEdges() - 1);
        return true;
      }
    }
    return false;
  }

  /**
   * this gives a list of vertices in the graph and their adjacencies
   *
   * @return returns a string describing this graph
   */
  public String toString() {
    String s = "    ";
    for (int i = 0; i < this.numberOfVertices(); i++) {
      s = s + String.valueOf(i) + " ";
    }
    s = s + " \n";

    for (int i = 0; i < this.numberOfVertices(); i++) {
      s = s + String.valueOf(i) + " : ";
      for (int j = 0; j < this.numberOfVertices(); j++) {
        s = s + String.valueOf(this._adjacency[i][j]) + " ";
      }
      s = s + "\n";
    }
    return s;
  }
}